The present invention relates to a scrolling color projector, and more specifically to the alignment of the optical and the electrical scan in a scrolling color projector.
A scrolling color projector produces full color images from a single light modulator by illuminating a liquid crystal panel with multiple stripes of colored light (red, green, blue) that continuously scroll, from top to bottom, over the liquid crystal panel. In order to scroll the multiple stripes of colored light over the liquid crystal panel, the strolling color projector includes a scanner for each color of light to be scrolled over the liquid crystal panel. Each scanner includes a prism connected to the shaft of a motor. The motor controls rotation of the prism. Also attached to the motor is a precision optical encoder which provides information regarding the position of the motor shaft, and correspondingly the rotation of the prism and the scan of each stripe of colored light on the panel.
The precision optical encoder provides information for control of the motor and correspondingly for control of the prism. The phase and rotation of the prism are important because each stripe of colored light must be projected and scrolled on the liquid crystal panel at specific times in relation to video information (electrical scan) that is also provided to the liquid crystal panel. That is, the red, green and blue stripes of light must be present on a line of the display concurrent with the presentation of the corresponding video information. The optical encoder serves to synchronize the phase of rotation of the prism (the scan of the color stripes) with the presentation of the video information. As a result, each stripe of light, as it is being scrolled down the liquid crystal panel, appears on a particular display line coincident with the corresponding video information (electrical scan) for that color of light. The prior art systems impose strict geometrical tolerances on parts during manufacture and assembly to assist in ensuring that the scan of the colored light is synchronous with the video signal (electrical scan). This includes a very accurate mounting of the prism on the motor shaft relative to a reference position of the motor.
A drawback to the prior art systems is that the precision optical encoder is very costly. Typically the optical encoder costs more than the entire scanner, i.e., more than the cost of the prism and the motor together. In addition, the imposition of strict geometrical tolerances on parts during manufacture and assembly adds to the cost of the system. It would therefore be beneficial to provide alignment of the optical and the electrical scan in a scrolling color projector without the use of an external precision optical encoder and strict geometrical tolerances on parts.
It is an object of the present invention to provide a method and apparatus for alignment of the optical and the electrical scan in a scrolling color projector which does not use an optical encoder.
It is a further object of the present invention to provide a method and apparatus for alignment of the optical and the electrical scan in a scrolling color projector which is less expensive than prior art optical and electrical alignment systems.
It is still a further object of the present invention to overcome inherent disadvantages of known methods and apparatus for alignment of the optical and the electrical scan in scrolling color projectors.
In accordance with one form of the present invention, a scrolling color projector for displaying an image on a screen includes a light source for generating an input light, a color splitter for at least one of transmitting and reflecting the input light emitted from said light source to split the light into at least first and second colors, at least a first color scanner including a motor and a prism for receiving as an input the first color of the input light. The motor rotating the prism to provide a scan of a first color scanner output signal on a display. The device also includes a motor controller which controls a rotation of the motor of the at least first color scanner. The motor controller accessing a reference phase offset value indicative of a difference in phase between the scan of the first color scanner output signal and an electrical scan of the display. The motor controller being responsive to the reference phase offset value to alter the rotation of the motor such that the scan of the first color output signal is in phase with the electrical scan of the display.
In accordance with another form of the present invention, a method of aligning the optical and electrical scan in a scrolling color projector includes providing a reference phase signal indicative of timing information for presentation of an optical scan and an electrical scan to a light valve, providing an optical scan and an electrical scan on the light valve in accordance with the reference phase signal, determining a difference in phase between the optical scan and the electrical scan on the light valve, storing the difference in phase between the optical scan and the electrical scan, and providing the optical scan to the light valve based on a combination of the difference in phase and the reference phase signal and providing the electrical scan to the light valve based on the reference phase signal.
A preferred form of the method and apparatus for alignment of the optical and the electrical scan in a scrolling color projector as well other embodiments, objects, features and advantages of the present invention will become readily apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings.